Study on the mechanism of CO chemical looping combustion over Fe-Based oxygen carriers with unsaturated coordination environments

IF 5.6 2区工程技术 Q2 ENERGY & FUELS

Journal of The Energy Institute Pub Date : 2024-08-31 DOI:10.1016/j.joei.2024.101809

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Abstract

It is crucial to study the Fe-O coordination environment due to oxygen defects for elucidating the dynamic active center during CO chemical looping combustion with hematite. In this work, Fe-based oxygen carriers with varying oxygen vacancy concentrations were firstly synthesized by direct thermal decomposition of ferric nitrate and subsequently evaluated through fixed-bed experimentation. It was showed that the reactivity of oxygen carriers produced by calcination at 700 °C exhibited a higher CO conversion rate due to the moderate oxygen vacancy concentration. Then, density-functional theory (DFT) calculations were conducted to examine the impact of oxygen vacancies. The results indicated that the formation of oxygen vacancies exhibited a proximity effect, resulting in the emergence of various Fe-O coordination environments. The low coordination number of Fe-O enhances the reactivity of the lattice oxygen and significantly lowers the activation energy barrier for the oxidation of CO to CO₂. Furthermore, the effect of oxygen vacancies on the migration of bulk phase oxygen was also investigated. It was shown that the migration barriers of bulk oxygen increased with the concentration of oxygen vacancies, resulting in a reduction in the oxygen supply rate. Moderate concentration of oxygen vacancies facilitates CO oxidation by aligning surface catalysis with the oxygen migration rate. This evidence suggests that the Fe-O coordination environment and oxygen vacancy concentration serve as key factors in controlling in controlling CO oxidation over Fe-based oxygen carriers.

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具有不饱和配位环境的铁基氧载体上的一氧化碳化学循环燃烧机理研究

研究氧缺陷导致的 Fe-O 配位环境对于阐明赤铁矿与 CO 化学循环燃烧过程中的动态活性中心至关重要。在这项工作中，首先通过直接热分解硝酸铁合成了不同氧空位浓度的铁基氧载体，随后通过固定床实验对其进行了评估。结果表明，由于氧空位浓度适中，在 700 °C 煅烧产生的氧载体具有更高的 CO 转化率。然后，进行了密度泛函理论（DFT）计算，以研究氧空位的影响。结果表明，氧空位的形成具有邻近效应，导致出现了各种 Fe-O 配位环境。低配位数的 Fe-O 增强了晶格氧的反应活性，并显著降低了 CO 氧化为 CO2 的活化能势垒。此外，还研究了氧空位对体相氧迁移的影响。结果表明，随着氧空位浓度的增加，体相氧的迁移障碍也随之增加，导致供氧率降低。适度的氧空位浓度可使表面催化作用与氧气迁移率保持一致，从而促进 CO 氧化。这些证据表明，Fe-O 配位环境和氧空位浓度是控制铁基氧载体氧化 CO 的关键因素。

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来源期刊

Journal of The Energy Institute 工程技术-能源与燃料

CiteScore

10.60

自引率

5.30%

发文量

166

审稿时长

16 days

期刊介绍： The Journal of the Energy Institute provides peer reviewed coverage of original high quality research on energy, engineering and technology.The coverage is broad and the main areas of interest include: Combustion engineering and associated technologies; process heating; power generation; engines and propulsion; emissions and environmental pollution control; clean coal technologies; carbon abatement technologies Emissions and environmental pollution control; safety and hazards; Clean coal technologies; carbon abatement technologies, including carbon capture and storage, CCS; Petroleum engineering and fuel quality, including storage and transport Alternative energy sources; biomass utilisation and biomass conversion technologies; energy from waste, incineration and recycling Energy conversion, energy recovery and energy efficiency; space heating, fuel cells, heat pumps and cooling systems Energy storage The journal''s coverage reflects changes in energy technology that result from the transition to more efficient energy production and end use together with reduced carbon emission.